Percutaneous Transluminal Angioplasty (PTA) is a medical procedure for widening a stenosis or constriction of a bodily passage. The most common application is to widen the passage of a blood vessel, such as an artery, which has been constricted by the build-up of cholesterol fats or atherosclerotic plaque. When this medical procedure is applied to a coronary artery, it is referred to as Percutancous Transluminal Coronary Angioplasty (PTCA).
Typically, a tip mounted balloon of a balloon catheter is advanced over a guidewire to the stenosis. Once the balloon catheter is properly positioned, the balloon is inflated to compress the plaque against the vessel walls and widen the stenosis. Problems occur, however, when the dilatation of the occlusion forms fissures, flaps and/or dissections which may ultimately cause reclosure or restenosis of the vessel.
To maintain vessel patency and/or strengthen the area undergoing angioplasty or other treatment, an intravascular prosthesis may be employed. These devices are usually introduced percutaneously, transported transluminally and positioned at a desired location within the widened stenosis of the patient. One form of an intravascular prosthesis is a radially expandable stent device which is typically positioned at the tip of a balloon delivery catheter in a crimped condition. When the tip of the delivery catheter apparatus and the crimped stent are properly positioned at the desired location or the stenosis, the balloon is expanded to implant the stent in the widened vessel. In some instances, expansion of the balloon portion of the delivery catheter can simultaneously compress the plaque at that location and expand the stent to its proper implantation size. The balloon portion of the catheter is then deflated and withdrawn from the vessel, leaving the implanted radioactive stent as a permanent scaffold and as a deterrent to tissue growth in order to reduce the chance of restenosis.
More recently, these stents have been embedded or implanted with radioisotopes so that they emit predictable amounts of radiation into the widened vessel and immediate surrounding area. The nature of these radioactive devices is that regrowth of the tissue can be reduced by the radiation, an effect which is highly beneficial in preventing restenosis of the vessel.
Although these radioactive stents only emit relatively low levels of radiation, direct contact with the stent by physicians, laboratory technicians, and other personnel should be avoided. As a result, shielding devices 10 such as those shown in FIGS. 1A and 1B have been developed to enable the safe transportation and handling of radioactive stent 11 and/or a stent delivery catheter apparatus 12. Typical of these shield devices 10 is disclosed in U.S. Pat. No. 5,605,530 entitled "System for Safe Implantation of Radioisotope Stents" which is incorporated by reference in its entirety.
These radioactive shield devices 10 typically include one piece main body portions 13 having longitudinally extending central lumens 15 therethrough. Positioned in these lumens 15 in a retracted condition (FIG. 1A) are the stent delivery catheter apparatus 12 and crimped radioactive stent 11 for shielding thereof. Accordingly, this one-piece configuration enables safe transportation and handling of the radioactive stent before being inserted into the vessel.
The radiation shield device 10 further preferably includes a distal proboscis 16 and a proximal threaded section 17 which operates as a Tuohy-Borst fitting 19 onto which a nut 18 can be screwed. When the expandable balloon 20 of the delivery catheter and the distal mounted radioactive stent 11 are retracted in the central lumen 15 of the shield device 10 (FIG. 1A), a shield nut 18 may be tightened down on proximal threaded section 17, thereby frictionally coupling the stent delivery catheter apparatus 12 therein.
To insert the stent delivery catheter apparatus 12 and stent 11 into a vessel (not shown), the proboscis 16 of the shield device 10 is preferably inserted into another Tuohy-Borst fitting 21 of a guiding catheter. This union may be provided by a Y-adapter 22 having an adapter nut 23 tightened to the threaded end 24 to functionally couple and fluid seal the radiation shield device to the Y-adapter. Subsequently, the proximal shield nut 18 may be loosened to enable the mounted stent 11 and the delivery catheter apparatus 12 to be forwardly advanced (FIG. 1B) into a passage 25 of the Y-adapter 22 and into the vessel as a unit.
While this one-piece shield device is most adequate to shield personnel from radiation exposure from the radioactive stent, several problems are inherent in the design. For example, when the radiation shield device 10 is mounted to the Y-adapter 22, and the delivery catheter is slideably inserted through the central lumen of the shield device and the passage 25 of the Y-adapter, the radiation shield device cannot be removed or separated from the delivery catheter apparatus 12 since the diameter of the central lumen is not sufficiently large to enable the proximal manipulating end of the catheter apparatus (not shown) to slide therethrough. Consequently, the depth of insertion of the delivery catheter is limited to the proximal end of the radiation shield device (i.e., the Tuohy-Borst fitting 19) rather than the proximal end of the Y-adapter 22 (i.e., the Tuohy-Borst fitting 21). Therefore, the useable length of the catheter 12 is decreased. Increasing the length of the catheter apparatus to compensate for the decrease of insertion depth may be problematic since any increase in length may incrementally reduce the ability to precisely control the stent placement. This configuration also limits the physicians choice of delivery catheters to only those provided with the stent.
Moreover, even should a length increase be unnecessary, manipulation of the catheter apparatus is still more difficult since the surgeon must now control the catheter from relatively cumbersome shield device as compared to the smaller proximal end of the Y-adapter. This is especially true in instances where the shield device 10 has been decoupled from the Y-adapter during stent deployment. The mere weight and bulkiness of the shield device 10 dangling from the catheter apparatus significantly reduces maneuverability and manipulation of the catheter. In fact, in some instances, care must be observed so that the weight of the shield device 10 does not retract the stent assembly from the vessel.
Another problem associated with this arrangement is that after the stent delivery catheter apparatus 12 and the mounted radioactive stent 11 have been passed through the central lumen 15 of the shield device 10 into the passage of the Y-adapter, it is difficult to reinsert the catheter apparatus and the stent back into the central lumen of the shield device 10, should this be necessary to abort the deployment procedure. Therefore, there is a need to enable removal of the radiation shield device from the delivery catheter apparatus during deployment of the stent.